Conventional non-toxic shotshells currently in use for hunting and target shooting have evolved over the past several years in response to changing environmental and economic requirements. One such significant change was the shift from the use of toxic lead (Pb) shot or pellets for waterfowl hunting to other, less toxic, materials. Because of its relatively low cost and wide availability, one choice of a material for non-toxic shotgun shot is steel, which may be forged and/or swaged into tough spheres from drawn wire and then ground to a spherical shape.
While steel may provide some benefits as a replacement for lead shot, it also has its limitations. Among others, these limitations include a density that is significantly less than that of lead shot and a tighter shot pattern. The first difference may make it more difficult to reach targets at a distance and/or decrease the effective range of the shot, while the second difference may make it more difficult to hit a moving target and/or closer targets.
While all hunters must contend with the properties of steel shot, more experienced hunters, who formerly utilized higher density, loosely-patterning lead shot have been particularly challenged in attempting to adjust to the attributes of spherical steel shot. Clinics have been, and continue to be, held around the world by such organizations as CONSEP (Cooperative North American Shotgunning Education Program) to teach hunters how to use steel shot more effectively, with the goal of increasing hunter proficiency. Obviously, only relatively small numbers of shooters can be personally tutored in this manner. Thus, the availability of an improved type of shotshell would aid significantly in achieving the underlying goal of improving hunter proficiency over a much larger constituency.
The greater shot pattern density of steel shot may be due to the increased hardness of the shot, which resists deformation by setback forces when a shot shell containing the shot is fired. In contrast, soft lead shot may be deformed significantly by these setback forces, producing a plurality of flat areas or facets on the shot surface. These facets may cause anomalous spinning of the pellets, causing them to deviate from a normal trajectory under the influence of the so-called Magnus effect, and broadening the spread of the shot pattern (i.e. decreasing the pattern density) at a given distance when compared to steel shot. Lead shot also has been shown to produce a longer shot pattern in the direction of shot motion when compared to steel shot.
The pattern of pellets crossing an impact region of a plane perpendicular to the line of flight of the shot, which may be referred to as the shot stream, is most dense close to the gun and less dense as the stream travels down range (i.e., away from the gun/shooter). This phenomenon may be visualized as a distribution of pellets moving away from the gun within a conical volume of space. Tighter patterns may be characterized by a smaller cone apex angle, while wider patterns may be characterized by a larger cone apex angle. A tighter pattern may be additionally characterized by a higher density of shot pellets within the impact region, while a wider pattern may be characterized by a lower density of shot pellets within the impact region. With this in mind, a shot pattern may be quantified by the percentage of the total number of shot pellets that are contained within a circle of a given diameter at a given distance from the shooter. For example, a 90%, 20-yard pattern diameter of 24-inches suggests that, at 20-yards from the shooter, 90% of the shot pellets will be contained within a 24-inch diameter circle. Shot patterns also may be characterized in terms of their dispersion, or spread, which may be related to the pattern diameter discussed above.
While modern shotshells loaded with steel shot may perform adequately at ranges beyond approximately 30 yards, the shot patterns may be too tight (i.e. too dense) at shorter ranges to be effective. Depending on the situation, it may be desirable to manufacture shotshells with shot patterns optimized for shorter distances, such as 0 to 30 yards, shotshells with shot patterns optimized for longer distances, such as distances greater than 30 yards, as well as multi-distant and/or multimodal shotshells optimized for shooting over a plurality of distances, or ranges of distances, such as distances of 5-100 yards, including distances of 10-70, 15-60, and 20-40 yards.
The tight shot patterns that may be inherent with the use of conventional steel shot may result in overkill. By overkill, it is meant that there may be no benefit in striking a target with more than the required minimum number of lethal pellets, especially if redundant numbers of pellets do nothing to expand the effective area of the pattern and/or cause unnecessary damage to the target. Thorough discussions of this and other technical aspects of patterning requirements are presented in two separate issues of Sporting Clays magazine (Vol. 10—No. 12—Issue 84, pp. 22-31, December, 1998 and Vol. 11—No. 1—Issue 85, pp, 38-70, January, 1999) by Tom Roster. While the prior art reveals various attempts to manipulate shot patterns, one must appreciate the large degree of shot stream dispersion that must be obtained in order to significantly impact the ability of a hunter to hit a short-range (less than 30 yards) target. If shot pellets travel within conical volumes of space, planar patterns may be mathematically estimated for specific shotshell designs for any given target diameter at any given range, once a pattern for some known target diameter (e.g., 30-inch) at some known range (e.g., 40 yards) has been empirically determined. For example, a pattern of 75% of pellets in a given shotshell load striking within a 30-inch diameter circle at 40 yards (a popular industry standard test) would exhibit a corresponding 75% pattern within a 15-inch diameter circle at 20 yards. While this example of a short-range pattern may be considered overly tight under certain circumstances, it may be quite typical of conventional shotshells loaded with spherical steel shot.
From another quite different perspective, one might wish to estimate the degree of shot dispersion necessary to obtain a 90%, 25-yard pattern diameter of 30 inches. This would imply a corresponding 90%, 40-yard pattern diameter of (40/25)×30=48 inches. In this case, only about 90%×(30/48)2=35% of the pellets would fall within a 30-inch diameter circle at 40 yards. As shown herein, obtaining sufficiently dispersive short-range patterns may require specialized pellet shapes and/or methods.
Historically, several different types of shotshells have been developed specifically for the purpose of modifying shot patterns. Various approaches have been tried, including placing plastic structures in the center of the shot column (Spred-R™ product by Polywad, Inc.) and using relatively small, high drag, spherical shot for swatter loads.
The Spred-R™ design simply effects a shift of a small portion of the pellets in the pattern from the dense, central core region (generally associated with a Gaussian shot distribution) outward to the fringe area of a typical 40-yard, 30-inch diameter pattern, thereby improving pattern uniformity, with little or no impact on effective range. Similarly, a limitation inherent in swatter loads is that, while useful at close range, effectiveness beyond about 25 yards is generally inadequate due to the small shot sizes employed. A typical hunter in a blind overlooking waterfowl decoys has no way of knowing at what range an initial opportunity will present itself. Therefore, shells designed only for close ranges may be of limited usefulness and may even decrease shooting proficiency if used improperly. In addition, the relatively small shot sizes used is in swatter loads may cause game meat containing such fine shot to be unpleasant or difficult to eat, resulting in wasteful loss of game.
U.S. Pat. No. 6,202,561 to Head et al. (the '561 patent) discloses modifying shot patterns by mixing combinations of steel spheres and other, higher-density spheres made from materials such as tungsten, bismuth, or copper. These spheres may be contained within the shotshell as layered mixtures of various spherical shot types with varying densities to obtain a combination of long-range/short-range performance.
This approach takes advantage of the density×diameter fluid drag relationship for spherical pellets, wherein the fluid drag forces are inversely proportional to the product of the density of the pellet and the diameter of the pellet, allowing similar diameter pellets of different densities to have different effective ranges. However, the '561 patent only addresses shot densities that are equal to or greater than the density of steel (7.8-7.9 g/cc). Not only are the differences in pattern dispersion attributed to differences in shot density (in the range of 7.9-11.0 g/cc) and shot diameter too small to significantly change short-range pattern diameter; but, as discussed herein, conventional steel patterns are already too tight to provide effective short-range shooting efficiency. Increasing pellet density by using the more costly (denser) metals, such as tungsten, bismuth, or copper, only exacerbates this short-range pattern diameter problem.
A shotshell described in printed advertisements and on websites by ATK/Federal Cartridge and sold under the BLACK CLOUD™ mark features a special shot cup (the FLITE CONTROL™ cup) that is believed to have been designed to tighten normal steel shot patterns. Included in this shotshell is a mixture of ordinary steel spheres and “belted spheres” of steel marketed as FLIGHT STOPPER™ shot. The latter shape is purported to increase wound trauma in game.
For a particular target, there exists an optimal impact region or shot pattern diameter, as well as an optimal density of shot pellets within that impact region. As discussed herein, this impact region diameter may be a function of both the distance from the gun and the ballistic characteristics of the pellets in flight. Since a target may present itself at a variety of distances from the gun, the ability to tailor the ballistic characteristics of the pellets in order to improve and/or select a specific shot pattern density within the impact region may be desirable.